Formalin is water­based­solution of formaldehyde. It is used as preservative in anatomy,bio­monitoring and many other laboratories. The present study aimed to determine Threshold odor number (TON)for formalin. TON is the greatest dilution of sample with odor free water at which a definite perceptible odor is achieved.The test was conducted with a panel of 20 individuals which were subdivided into 2 panels; panel 1­ lab workers and panel 2­ non lab workers. These individuals were exposed to varied concentrations of formalin ranging from 0.01 to 0.1% with blanks inserted in series at regular intervals to avoid tiring the senses of testers. The observations were recorded by indicating whether odor is noted or not in each test bottle. The TON for lab workers was observed to be 1333 while for non­lab workers it was 2000.As per the findings of test, it can be concluded that increase in TON indicates more sensitivity towards formalin.The observed difference in TON value is due to some day to day exposure of the testers of panel 1 to formalin, thereby having olfactory adaptation to the odorant. As formalin is toxic even in very low concentration, therefore, use of mask while working with formalin in lab is recommended for occupational health of lab workers. This test has been standardised for formalin only but is equally applicable to determine TON for other chemicals used in laboratories and to check the quality of water bodies.

Keywords: Formalin; Occupational Health; Perceptible Odor Limit; Threshold Odor Number.